High-power short-pass total internal reflection filter

Patent metadata

Field	Value
Publication number	US-10691024-B2
Application number	US-201816165799-A
Country	US
Kind code	B2
Filing date	Oct 19, 2018
Priority date	Jan 26, 2018
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

Abstract

An apparatus for generating filtered light may include a broadband illumination source configured to generate broadband illumination and a total internal reflection (TIR) filter formed from a material at least partially transparent to the broadband illumination. The TIR filter may include one or more input faces oriented to receive the broadband illumination. The TIR filter may further be oriented to reflect wavelengths of the broadband illumination beam below a selected cutoff wavelength on one or more filtering faces as filtered broadband illumination and provide the filtered broadband illumination beam through one or more output faces. The cutoff wavelength may further be selected based on total internal reflection on the one or more faces.

First claim

What is claimed:

1. An apparatus for generating filtered laser-sustained plasma light comprising:
one or more pump sources configured to generate pump illumination;
a focusing element arranged to focus the pump illumination onto a plasma target to generate a plasma that emits broadband illumination;
a collector element arranged to collect the broadband illumination from the plasma; and
a total internal reflection (TIR) filter formed from a material at least partially transparent to the broadband illumination, the TIR filter including a single planar input face oriented to receive the broadband illumination and one or more filtering faces oriented to retroreflect wavelengths of the broadband illumination beam below a selected cutoff wavelength as filtered broadband illumination back through the single planar input face, wherein the cutoff wavelength is selected based on total internal reflection on the one or more filtering faces, wherein rejected broadband illumination beam exits the TIR filter through one or more output faces positioned opposite of the single planar input face.

2. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the broadband illumination comprises:
continuous-wave light.

3. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the broadband illumination comprises:
pulsed light.

4. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the plasma target comprises:
a gas plasma target, wherein a volume of the gas plasma target is contained within a gas containment structure having one or more transparent elements at least partially transparent to the pump illumination and the broadband illumination.

5. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the plasma target comprises:
a solid plasma target.

6. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the plasma target comprises:
a liquid plasma target.

7. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the one or more filtering faces comprise:
a grooved surface including a periodic distribution of angled faces distributed along a distribution direction, the angled faces including a first set of groove faces interlaced with a second set of groove faces, wherein the first set of groove faces intersect with the second set of groove faces at a common apex angle.

8. The apparatus for generating filtered laser-sustained plasma light of claim 7 , wherein the one or more filtering faces comprise:
two or more triangular prisms having apexes with the common apex angle arranged in a linear distribution, wherein faces of the two or more triangular prisms opposing the apexes form the single planar surface.

9. The apparatus for generating filtered laser-sustained plasma light of claim 8 , wherein edges of the two or more triangular prisms are fused to provide a single element forming a Fresnel prism array.

10. The apparatus for generating filtered laser-sustained plasma light of claim 7 ,
wherein the one or more filtering faces comprise:
the first and second sets of groove faces.

11. The apparatus for generating filtered laser-sustained plasma light of claim 7 , wherein the common apex angle is 90 degrees.

12. The apparatus for generating filtered laser-sustained plasma light of claim 1 , further comprising:
an out-of-band coupler positioned proximate to the one or more filtering faces, wherein the out-of-band coupler receives wavelengths of the broadband illumination transmitted through the one or more filtering faces and directs the received wavelengths away from the TIR filter.

13. The apparatus for generating filtered laser-sustained plasma light of claim 12 , wherein a separation distance between the one or more filtering faces and the out-of-band coupler is selected such that the out-of-band coupler is configured to receive the wavelengths of broadband illumination transmitted through the one or more filtering faces by evanescent-wave coupling.

14. The apparatus for generating filtered laser-sustained plasma light of claim 1 , further comprising:
an anti-reflective coating disposed on the one or more filtering faces having an operational range including wavelengths of the broadband illumination beam above the selected cutoff wavelength.

15. The apparatus for generating filtered laser-sustained plasma light of claim 1 , further comprising:
an anti-reflective coating disposed on at least one of the one or more input faces or the one or more output faces having an operational range including at least wavelengths below the selected cutoff wavelength.

16. The apparatus for generating filtered laser-sustained plasma light of claim 1 , further comprising:
an anti-reflective coating on at least one of the one or more filtering faces, at least one of the one or more input faces, or at least one of the one or more output faces.

17. The apparatus for generating filtered laser-sustained plasma light of claim 16 , wherein the anti-reflective coating comprises:
at least one of a dielectric-stack anti-reflective coating, a graded refractive index coating, or a nano-structured anti-reflective coating.

18. The apparatus for generating filtered laser-sustained plasma light of claim 1 , further comprising:
a rotational stage securing the TIR filter, wherein the cutoff wavelength is selectable by rotating the TIR filter to adjust an incidence angle of the broadband illumination beam on the one or more filtering faces.

19. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the selected range of wavelengths of the broadband illumination beam reflected from the one or more planar faces comprises:
a range of approximately 100 nanometers to approximately 220 nanometers.

20. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the selected range of wavelengths of the broadband illumination beam reflected from the one or more planar faces comprises:
a range of approximately 115 nanometers to approximately 150 nanometers.

21. The apparatus for generating filtered laser-sustained plasma light of claim 1 , wherein the selected range of wavelengths of the broadband illumination beam reflected from the one or more planar faces comprises:
a range of approximately 115 nanometers to approximately 130 nanometers.

Assignees

• Kla Tencor Corp

Inventors

• Zhao Wei
• Bezel Ilya

Classifications

• H05H1/24

  Generating plasma {(nuclear fusion reactors G21B1/00; gas-filled discharge reactors H01J37/32)} · CPC title

• H01J65/042

  by an external electromagnetic field · CPC title

• G03F7/70033 Primary

  by plasma extreme ultraviolet [EUV] sources · CPC title

• H01J61/025 Primary

  Associated optical elements · CPC title

• H01J23/033

  Collector cooling devices · CPC title